Metallic lead frames and sealing resins are mainly used for semiconductor packages, where copper alloys are frequently used for the lead frames and epoxy resins are the mainstream of the sealing resins.
In addition, for heat dissipation of a semiconductor package, a copper plate or a copper alloy plate is sometimes used as a material of a component called a heat spreader, and the lead frame and the heat spreader are fixed with a sealing resin.
In a product in which metal materials using copper and a copper alloy and a resin are joined in such a way, the adhesion often comes to be an issue, and as measures for improving the resin adhesion, methods for roughening treatment of the surfaces of the lead frame and the heat spreader are adopted for attaining the anchor effect.
However, the problem in these methods is in that, in a semiconductor package of the QFN (Quad Flat Non-Lead) type for example, the connection terminals are uncovered on the lower surface of the sealing resin, and roughening treatment of the lower surface of the metallic material may cause leakage of the resin, whereas the roughening treatment makes it difficult to peel off the leaked resin. Therefore, conventionally, there have been proposed methods for making roughening treatment locally, but these processing methods involve the problem of increased cost.
Further, since high-temperature heating of the copper material progresses copper oxidation on the roughened surface to easily cause the oxide film to peel off and decreases the resin adhesion as compared with before heating, the roughening treatment of the copper material therefore has not yet obtained sufficient reliability for a semiconductor package.
Conventionally, the art shown in Patent Document 1, Patent Document 2, and Patent Document 3 have been disclosed as alternatives to these roughening treatments.
Patent Document 1 discloses, as a method for improving the adhesion between a heat sink and a resin adhesive in the heat sink of an electronic component such as a semiconductor device, immersing in a solution containing 0.001% or more of an aminosilane compound a metal plate or strip material with Ni or Ni alloy plating, to form an aminosilane compound coating on the outermost surface of a portion that is to be bonded to the resin with the adhesive.
Patent Document 2 discloses forming a nickel plating layer on a copper plate as a substrate, forming thereon a coating layer of silane coupling agent or a polyacrylic acid film to make the outcome as a heat sink for a semiconductor, bonding thereto a semiconductor element and a printed circuit board, and sealing the semiconductor element with a transfer molding resin, to obtain a heat sink for a semiconductor excellent in adhesion to adhesive resin.
Patent Document 3 discloses a copper or copper alloy plate or strip in which a silane compound coating of 0.5 mg/m2 or more in terms of Si adhered amount is formed on the outermost surface and an oxide film having a thickness of 1000 to 2000 Å is formed on the layer beneath, wherein aqueous solution of silane coupling agent at 40° C. to 60° C. is applied to the surface of the copper or copper alloy plate or strip to form the silane compound coating on the surface and then heat treatment is made to form the oxide film of the copper or copper alloy plate or strip with the thickness of 1000 to 2000 Å on the layer beneath the silane compound coating, thereby to obtain a copper alloy plate or strip material excellent in adhesion to resin.
The surface treatment of copper and copper alloy strips by these conventional chemical method makes it difficult to sufficiently improve the adhesion to the resin, and a technique for improving the adhesion between the lead frame and the resin is still required.